Have No Fear, CCI is Here

Many manufacturers make the mistake of fitting the capacity and operating characteristics of their valves to stroke lengths permitted by the actuation systems they choose, which often results in poor valve control and system instability. This was the case at Carolina Power & Light Company’s (CP&L’s) Cape Fear Steam Electric Station, whose conventional ported-cage valve – sized for delta-p = 50 psig at full flow – was misapplied, resulting in over-capacity, severe vibration at low flows, and continuous actuator oscillation when searching for position.

The short stroke length of the feedwater regulator valve at Cape Fear upset the boiler and provided wide, unstable flows with each small signal for a flow change. CCI’s standard feedwater regulator valve with DRAG® technology, however, solved these problems at the Raleigh , North Carolina once-through steam turbine power plant, providing high rangeability and a longer valve stroke.

Although CCI’s valve is nearly half the size of Cape Fear ’s old valve, its longer, 8-inch stroke provides a finer degree of control for each percentage of position change, resulting in extremely stable process control and improved stability for the whole system. The CCI solution also reduces Cape Fear ’s startup time, and as the new valve offers more accurate control of plant output, it boosts overall efficiency.

This classic DRAG® solution was customized to meet Cape Fear ’s specific requirements. Because the water pressure is higher flowing into the valve than out of the valve, CCI designed the disk stack with more right-angle turns to reduce velocity at the bottom and fewer turns at the top. The disk stack is also taller, providing for more range and more precise control. With this design, the single CCI DRAG® valve can handle both low and high flow to function as a combined startup and main valve, thereby eliminating the need for the startup valve.

When exploring its options for addressing its control valve problems, Cape Fear received an excellent reference from its sister plant, CP&L Robinson Station, whose Copes-Vulcan feedwater valve has a CCI DRAG® disk stack retrofit inside. CCI was able to retrofit the problematic control valve with DRAG® technology with the valve in place for a simple installation and impressive savings. Whether retrofit or replacement, the Carolina sister plants prove that CCI’s DRAG® technology offers unmatched performance in severe service control.

Published in SOLUTIONS Spring 2004